Chrome-steel.



CHILD HAROLD WILLS, 0F DETROIT, MICHIGAN.

CHROME-STEEL.

Specification of Letters Patent.

Patented Dec. 17, 191%.

e Drawing. Original application filed June 9, 1917, Serial No. 178,719 Divided and this application flied August 7, 1917. Serial No. 184,941.

from the use of chromium as an alloy are greatly increased, and the effect ofthe chromium greatly intensified, while, at the same time, certain of the undesirable effects incident to the use of the chromium are eliminated.

To illustrate, in chrome steel the chromium is added to increase the tensile strength and also to increase the penetration or depth of hardening on heat treatment. In so far as the physical properties of the steel are concerned, the increase in tensile strength obtained by the use of chromium is accompanied by loss or reduction in the amount of elongation, and furthermore, the use of chromium in fairly large percentages,

so to obtain corresponding increase in tensile 'spects, chrome steel would be desirable.

strength, necessitates 011 quenching because the steel in such case has a marked tendency to develop cracks and other imperfections when water quenched. It follows, therefore, that when the chromium is added in large quantities the'stcel is not quite so suitable for general commercial operations, and is not quite so good on all around steel.

Again in connection with the use of chromium to increase the depth of hardening, this result is accompanied by the increase in machining hardness and brittleness, which involves a corresponding increase in the cost of working, and renders the steel unsatisfactory and even entirely unsuitable for some classes of work for which, in all other rfi might here also be noted that chrome steels have a tendency to over-crystallization and,-

ichigan, have invented certain new and the temperature range of heat treatment is narrow. If this allowable narrow range be exceeded, the properties of the steel are greatly impaired, with resultant loss in manufacture and in service, to overcome which it has been customary to provide complicated regulating furnace equipment which, however, has not been found to produce uniformly satisfactory results.

My invention involves the addition to chrome steels of a powerful agent which shall not only. intensify the effect of the chromium itself, but also have an additive effect of its own with respect to the proper ties of the steel for which chromium is added, and which in addition shall have an independent eifect on those properties of the steel undesirably affected by the use of chromium. To accomplish these results I add to chrome steels molybdenum in percentages varying from a substantial fraction of 1% to about 1%. The resultant al- 10y may be termed a chrome-molybdenum steel, and l find that the addition of the molybdenum greatly increases the tensile strength and the elastic limit of the steel without the reduction in elongation normally resulting from the use of chromium alone. At the same time, increase in the depth of hardening is also obtained, but without corresponding increase in machinmg hardness and brittleness. The molyb denum therefore has an independent-effect 0n the machining hardness and brittleness and the elongation, for example, and has an intensifying effecton the other properties imparted by the chromium, as well as an additive effect of its own.

To illustrate the foregoing, attention is directed to the following comparative tables of tests conducted with 3/4 hexagon bars, quenched at 1560 F.-, and drawn at 1020 F., the first steel being a plain unalloyed carbon steel containing 23% carbon, .81% manganese, 021% phosphorus, 025% sulfur, and 25% silicon; the second steel having added thereto .60% chromium and no molybdenum; the third steel having added thereto no chromium and .70% molybdenum; and

the fourth steel having added thereto .60%

Upon comparing the first and second steels it will be seen that the addition of chromium causes a marked increase in tensile strength and elastic limit but substantially reduces the elongation 50%. The third steel, in which molybdenum only was added, shows a still greater increase in tensile strength and elastic limit, but with very little additional drop in the elongation, thus demonstrating that the molybdenum has an additive effect to tensile strength and elastic limit. In the fourth steel to which both chromium and molybdenum were added, it will be noted that the tensile strength and elastic limit are further increased, but that. elongation remains substantially the same, which demonstrates that the molybdenum intensifies the effect of the chromium and at the same time independently afiects elongation so as to prevent substantial reduction thereof.

In addition, the molybdenum has the effect of greatly increasing the temperature range of heat treatment without structural and chemical change such as would impair or destroy the properties of the steel. This is n advantage of great importance for the reason that the quality of the steel will run uniformly notwithstanding the impossibility of maintaining furnace temperatures uniform, and it is possible to forge at higher temperatures, to draw at higher temperatures and to refine the steel in one operation where two or more quenching operations are ordinarily necessary. The need of complicated regulating equipment and operators is also obviated and manufacture greatly simplified. The molybdenum does not have the tendency to segregate and appears to have the efiect of preventing the tendency of other alloys to segregate, as is the case with manganese where manganese is added to produce a chrome manganese steel for example. The molybdenum also overcomes the tendency of chrome steels to crystallize. Finally the molybdenum increases the resistance to alternating stresses and prevents the tendency in the chrome alloys containing larger percentages of chrome, to develop cracks when water quenched, thus making it possible to water quench such steels instead of oil quenching. The molybdenum also reduces the cost of manufacture in that it cuts down the amount of croppage'and grinding necessary because the tendency to piping and seaming is materially cut down.

The foregoing results are also obtained nasaeaa when molybdenum is added to chrome-nickel and to chrome-manganese steels, in each of which the tensile strength and the elastic limit are increased, without reduction in elongation and without corresponding increase in machining hardness. In addition to the other desirable advantages noted, the addition of molybdenum greatly increases the hold of use for the various chrome steels by rendering them more workable.

According to my invention 1 may use the molybdenum as a straight addition to intensify the effect of the chromium, and add to the qualities of the steel, or I may replace a portion of the chromium by a smaller percentage of molybdenum to obtain substantially the same results in so far as tensile strength and elastic limit are concerned. Stated in other words, the repacing of a portion of the chromium by the molybdenum will secure the same results, but without the undesirable eifects of the chromium.

The molybdenum should be used in small percentages as I find that if materially more than 1% be added, the steeldevelops undesirable characteristics. I prefer an analysis coming within the following proportions: carbon from .007?) to 55%; manganese from 20% to 1.25%; chromium from substantial fractions of 1% to 2%; silicon from .10% to 340%; and molybdenum from a substantial fraction of 1% to 1%.

In addition to the foregoing my invention has special reference to steel for case hardening purposes; that is to say, for articles in 100 which it is desired to have a tough center and a hard wearing surface, as for example, in gears, cams, cam shafts, roller bearings, valves, pins, and the like, such as used in automobile manufacture. In this connection 105 I have found that the molybdenum secures a case of deeper penetration, with carbon heavy at the surface and shading off gradually. The tendency to crystallization during case hardening is also greatly reduced, and because of the great increase in the range of heat treatment, refinement may be efi'ected more quickly and economically, the use of molybdenum making it possible to exceed the critical range for the case and refine the core and case at one quenching, without impairment of the case. In general, the steel is far superior to ordinary steels used for case hardened parts.

For steel for case hardened parts, I prefer 120 the following proportions of content: namely, carbon from 06% to 18%; manganese from 20% to .7 5%; chromium from a fraction to .75%; silicon from 10% to .4070; and molybdenum from a substantial 125 fraction of 1% to 1%.

I claim:

1. Steel containing carbon from 06% to 55%; manganese in traces up to 1.25%; chromium in substantial fractions of 1% to 130 magma 2.0%; silicon from '.10% to .4075; and molybdenum in substantial fractions of 1% to 1%; substantially as set forth.

2. Case hardening steel comprising the usual constituents and containing molybdenum as an added element in quantities not materially exceeding 1 per cent. characterized in that the refining of the core and case may be simultaneously accomplished.

3. Case hardening steel for articles of the class described containing carbOn from .O6% to .18%; manganese from 20% to .75%; chromium from a, fraction to .75%; silicon from .10% to 40%; and molybdenum from substantial fractions of 1% to about 1%; 15 substantially as set forth,

In testimony whereof I have hereunto signed my name.

CHILD HAROLD WILLS. 

